Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B32—LAYERED PRODUCTS
  • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
  • B32B27/00—Layered products comprising a layer of synthetic resin
  • B32B27/32—Layered products comprising a layer of synthetic resin comprising polyolefins
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B32—LAYERED PRODUCTS
  • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
  • B32B25/00—Layered products comprising a layer of natural or synthetic rubber
  • B32B25/04—Layered products comprising a layer of natural or synthetic rubber comprising rubber as the main or only constituent of a layer, which is next to another layer of the same or of a different material
  • B32B25/08—Layered products comprising a layer of natural or synthetic rubber comprising rubber as the main or only constituent of a layer, which is next to another layer of the same or of a different material of synthetic resin
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B32—LAYERED PRODUCTS
  • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
  • B32B27/00—Layered products comprising a layer of synthetic resin
  • B32B27/06—Layered products comprising a layer of synthetic resin as the main or only constituent of a layer, which is next to another layer of the same or of a different material
  • B32B27/08—Layered products comprising a layer of synthetic resin as the main or only constituent of a layer, which is next to another layer of the same or of a different material of synthetic resin
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B32—LAYERED PRODUCTS
  • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
  • B32B27/00—Layered products comprising a layer of synthetic resin
  • B32B27/18—Layered products comprising a layer of synthetic resin characterised by the use of special additives
  • B32B27/20—Layered products comprising a layer of synthetic resin characterised by the use of special additives using fillers, pigments, thixotroping agents
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B32—LAYERED PRODUCTS
  • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
  • B32B38/00—Ancillary operations in connection with laminating processes
  • B32B38/0012—Mechanical treatment, e.g. roughening, deforming, stretching
  • B32B2038/0028—Stretching, elongating
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B32—LAYERED PRODUCTS
  • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
  • B32B2305/00—Condition, form or state of the layers or laminate
  • B32B2305/02—Cellular or porous
  • B32B2305/026—Porous
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B32—LAYERED PRODUCTS
  • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
  • B32B2307/00—Properties of the layers or laminate
  • B32B2307/70—Other properties
  • B32B2307/724—Permeability to gases, adsorption
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B32—LAYERED PRODUCTS
  • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
  • B32B2307/00—Properties of the layers or laminate
  • B32B2307/70—Other properties
  • B32B2307/726—Permeability to liquids, absorption
  • B32B2307/7265—Non-permeable
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B32—LAYERED PRODUCTS
  • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
  • B32B2323/00—Polyalkenes
  • B32B2323/04—Polyethylene
  • B32B2323/046—LDPE, i.e. low density polyethylene
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B32—LAYERED PRODUCTS
  • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
  • B32B2323/00—Polyalkenes
  • B32B2323/10—Polypropylene
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B32—LAYERED PRODUCTS
  • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
  • B32B2555/00—Personal care

Definitions

• the invention relates to a method for producing a microporous multilayer film which is impervious to liquids but permeable to gases and more particularly to water vapor.
• the invention relates more particularly to a method for producing a microporous multilayer film which is impervious to liquids but permeable to water vapor by coextrusion of thermoplastic compositions consisting of mixtures of polymers and / or olefinic copolymers and optionally particulate fillers, each layer of the film having a specific composition.
• the invention also relates to a microporous multilayer film which is impervious to liquids and permeable to water vapor, as well as laminates associating said film with at least one nonwoven fabric and disposable hygiene articles, such as diapers for children, adult incontinence or feminine hygiene, using the microporous film and / or the rolled product.
• Polymer films are naturally impervious to liquids and water vapor and constitute a real barrier to these materials.
• barrier films When these barrier films are used as components of disposable sanitary articles, such as diapers for children or adult incontinence, or in articles of feminine hygiene, they can cause irritation of the skin, a certain discomfort, moisture can not escape the item when it is in use. For this reason, an extensive research effort has particularly developed in the field of films intended for the construction of children's diapers, for incontinent adults and feminine hygiene articles, on the breathability of the film, on its touch. textile, especially when it comes to the external (rear) film.
• microporosity of the films produced according to the known methods it can be carried out by numerous methods, including, for example, mechanical microperforation.
• the method most frequently used for the production of microporous films consists, in a first step, of using a mixture of polymers and inorganic fillers which is extruded (or extruded blown) in the form of a precursor film, then in a second step, to subject this precursor film to a stretching operation in the longitudinal direction and / or in the transverse direction, at a temperature lower than that of the melting point of the polymer mixture, to create a multiplicity of pores or micro-holes.
• Such pores have diameters small enough to prevent the passage of liquids, but allow the transfer of gas (water vapor) at transmission speeds ranging from the most moderate to very high.
• electron micrographs can be used to illustrate, for example, differences in the shape of the uniaxially or biaxially stretched films.
• the test of determining the velocity of water vapor transmission is a means for measuring the breathability of the film, i.e. the mass or volume of gas transferred through the thickness, for a unit of area and per unit of time, under well-defined environmental conditions.
• gas-permeable (respirable) and liquid-impermeable films may have a single layer or more recently multilayer structure.
• Films with multilayer structure are well known in the field of food packaging comprising an oxygen barrier. These films with a multilayer structure are intended to combine different families of polymers that are incompatible with one another, which therefore require, for their assembly into a film, the presence of functional polymers having a polar character.
• These films with a multilayer structure can be produced either by a process consisting of a coextrusion (direct or simultaneous) of all the layers, followed by their drawing, or by a method of assembly by rolling several layers (previously extruded or drawn), or else by an extrusion coating method on an already existing layer, such as a nonwoven fabric, followed by stretching.
• the US Patent 5,164,258 discloses a multilayer film permeable to water vapor which comprises outer layers made of a microporous hydrophobic polymeric material and a core layer made of a hygroscopic polymer material, exhibiting, when dry, a very large capacity of barrier to oxygen, but losing this property when it is wet.
• This multilayer film also has adhesive layers disposed between the outer layers and the core layer.
• This patent specifies that the transmission rate of water vapor for the outer layers should be about 500 g / m 2 / 24h, in order to be able to evacuate the moisture resulting from the sterilization treatment.
• the film with multilayer structure is specifically adapted to the application to the packaging (requiring an oxygen barrier) and can not be implemented in the field of sanitary or hygiene applications.
• the U.S. Patent 4,828,556 discloses a multilayer structure consisting of a breathable film of liquid barrier-forming polymer materials disposed between two layers of microporous nonwoven fabrics.
• This structure comprises a porous sheet, coated, by coating, with a polyvinyl alcohol film or laminated with a polyvinyl alcohol film previously produced.
• polyvinyl alcohol film acts both as an adhesive layer and as a water vapor permeable layer.
• the US Patent 4,758,239 also discloses a breathable liquid barrier multilayer structure which includes a first layer made of a porous nonwoven fabric and a second layer bonded to one of the faces of the first layer.
• This second layer is formed by a continuous film, made by coating with a water-soluble polymer material: this film is not microporous in that it does not have substantially pores, but it can be crossed, in its thickness, by the water molecules which are soluble in the film material, and which are transferred from one surface to the other of said film.
• the continuous film may be a pre-formed film made of a water-soluble polymer material which is laminated with the first layer of said structure, made of a porous nonwoven fabric .
• the water-soluble polymeric material is a polyvinyl alcohol.
• polyvinyl alcohols are known to be more difficult to process than polyolefins.
• films with multilayer structure breathable, but liquid-tight are described in the documents WO 98/58799 , WO 96/19346 , WO 99/14047 and WO 99/14262 .
• the invention has a number of objectives, to eliminate the aforementioned drawbacks.
• the permeability of the gas film in general will be expressed by the permeability of said film to water vapor.
• a first object of the invention is to create a method for manufacturing a multilayer film impervious to liquids and permeable to water vapor, which operates at high production speeds and which uses polyolefins as constituent materials of the invention. various layers.
• Another object of the invention is to create said method of manufacturing a film with a multilayer structure, impervious to liquids but permeable to water vapor, from a multilayer coextrusion, in such a way that exists a great ease of adaptation of the architecture of the various layers. More particularly, the creation of an asymmetrical architecture of the layers of the structure is, in the context of the invention, in order to incorporate, in the multilayer film, adhesion means for the subsequent assembly of said film with other structures, such as nonwoven fabric for example.
• Another object of the invention is to eliminate all the volatile materials present (moisture, air or other), in mixtures of raw materials, which could be released by heating, during extrusion, and which could disturb the formation controlled pores of the various layers of the microporous film.
• Another object of the invention is to optimize the breathability of the film with a multilayer structure, that is to say the transmission speed of the water vapor for the final structure, while maintaining the impermeability of the film to liquids.
• Another object of the invention is to achieve, according to said method, a thin film with a multilayer structure, impermeable to liquids and permeable to water vapor, however sufficiently resistant to tearing, which can be used as a rear film layers for children, incontinent adults and feminine hygiene articles, laminated to a nonwoven fabric, the resulting rolled product being used in the aforementioned articles.
• the invention also relates to a liquid-impervious, water-vapor permeable, multi-layered thin film used alone or laminated with a non-woven fabric, as a rear film for disposable sanitary articles for children. for incontinent adults and feminine hygiene items.
• Said layers "A", "B” and “C” are entirely composed of polyolefinic materials.
• the central layer "B" is formed of at least one homopolymer and / or a polyolefin copolymer and at least one particulate filler, and optionally one or more elastomers based on polyolefin.
• homopolymers or copolymers are chosen from the group comprising homo and / or copolymer polyethylenes, preferably linear low density polyethylenes and / or homo and / or copolymer polypropylenes.
• homo ethylene polymers or copolymers are selected from those having a density in the range 0.915 to 0.965 (ASTM 1505), and preferentially in the lower density range of 0.915 to 0.935.
• linear low density polyethylenes they have a density of between 0.890 and 0.940 and can be chosen from the group of copolymers of ethylene and of alpha-olefinic comonomers such as those of C4 to C10, obtainable for example by polymerization. catalytic in the presence of a catalyst, such as a metallocene or other modes.
• C4 to C10 comonomers are preferably selected from the group consisting of butene, pentene, hexene, 4-methylpentene, heptene, and octene.
• Homopolymeric or copolymeric propylene polymers include homopolymers of propylene, copolymers of propylene with ethylene, copolymers of propylene with C4 to C10 alpha-olefin comonomers.
• propylene copolymers one or more alpha-olefin comonomers may be used.
• the alpha-olefinic propylene copolymers must have an alpha-olefin content of between 0.1 and 40% by weight, and more preferably between 1 and 10% by weight.
• polypropylene copolymers are preferably selected from the group of ethylene-propylene copolymers.
• the polymers and / or copolymers of the central layer "B" are chosen such that the melt index measured by the "Melt Flow Index” (MFI) method is between 0.2 and 15 g / 10 min, measured according to the references of a load of 2.16 kg, a temperature of 190 ° C for polyethylenes and 230 ° C for polypropylenes with a standard orifice (standard ASTM D 1238).
• MFI Melt Flow Index
• the melt index can vary from 0.8 to 15 g / 10 min, and for the blown process from 0.2 to 10.0 g / 10 min. .
• the core layer "B” is preferably made from linear low density polyethylene.
• All these polymers or copolymers can be formulated with slip agents and antiblocking agents, as well as with antioxidants and stabilizers.
• the central layer "B" according to the invention also contains at least one particulate filler in a proportion of 30 to 80% by weight and preferably 45 to 55% by weight of the total of said particulate filler and of the polymer material.
• particulate fillers known in the state of the art, can come from any organic or inorganic materials having a low affinity for water naturally or by appropriate treatment and rigidity as opposed to the elasticity of the polymeric material.
• Organic particulate fillers may include, for example, polymers with a high melting point and / or high viscosity and whose particles have a size compatible with the process stretching step.
• polymers are, for example, polyethylenes, polypropylenes, polyamides, polyesters, high density polyurethanes and extremely high molecular weight.
• Inorganic particulate fillers may include metal salts, such as barium carbonate; calcium carbonate; magnesium carbonate; magnesium sulfate; barium sulfate; calcium sulphate, metal hydroxides, such as aluminum hydroxide; magnesium hydroxide, metal oxides, such as calcium oxide; magnesium oxide; titanium dioxide and zinc oxide, or other particulate materials, such as clay, kaolin, talc, silica, diatomaceous earth, glass powder, mica, of aluminum and zeolites.
• metal salts such as barium carbonate; calcium carbonate; magnesium carbonate; magnesium sulfate; barium sulfate; calcium sulphate
• metal hydroxides such as aluminum hydroxide
• magnesium hydroxide metal oxides, such as calcium oxide; magnesium oxide; titanium dioxide and zinc oxide, or other particulate materials, such as clay, kaolin, talc, silica, diatomaceous earth, glass powder, mica, of aluminum and zeolites.
• the inorganic particulate fillers are preferably selected from the group consisting of calcium carbonate, barium sulfate, silica, alumina, kaolin, and talc.
• Calcium carbonate is particularly preferred because of its economic cost, its whiteness, its inertia and its availability.
• Inorganic particulate fillers such as calcium carbonate
• a preferred coating is calcium stearate which is used in the diet. But, other coatings are possible.
• the amount of particulate fillers added to the polyolefins depends on the properties desired for the breathable film, which must have, among other things, good tear resistance, a sufficient water vapor transmission rate and sufficient elasticity.
• a film can not be sufficiently breathable when it is manufactured with a quantity of fillers of less than about 30% by weight of the polyolefin-filler composition.
• the minimum amount of 30% by weight of fillers is necessary to ensure the creation of a useful microporosity of the film during drawing.
• the films can not be used with a quantity of charges greater than about 80% by weight of the polyolefin-filler composition because larger amounts of filler can cause problems during mixing and cause problems. significant loss of breathability for the film.
• the amount of particulate fillers used in the composition of the layers according to the invention is between about 30% and 80% by weight, based on the cumulative amount of the polymeric material and the filler.
• the average diameters of the particulate fillers used in the invention are chosen between 0.5 and 5 ⁇ m, and preferably between 0.8 and 2.2 ⁇ m for the central layer "B", for films having a thickness of between 20 and 100 ⁇ m before stretching.
• the polymeric materials and fillers used in this invention can be mixed in various known ways.
• the elastomers used in the central layer "B" are chosen from the group consisting of ethylene-propylene rubbers (EPR), modified ethylene-propylene-diene rubbers (EPDM), styrene-butadiene-styrene (SBS), styrene-ethylene-butadiene-styrene (SEBS), styrene-butadiene rubber (SBR), styrene-isoprene-styrene (SIS), butyl rubber (BR), nitrile rubber (NBR), hydrogen-nitrile-butyl rubber and polyvinyl acetate; or used in accordance with a mixture, (either in a reactor or by extrusion), of semi-crystalline polymers selected from polyethylene and polypropylene with at least one other elastomer, such as for example polyethylene / ethylene-propylene rubber (PE / EPR), polyethylene / modified ethylene-propylene-d
• the elastomeric fraction is partially or completely cross-linked, or belongs to the group of polypropylenes (homopolymers) with amorphous and semi-crystalline blocks and copolymers of propylene / ethylene or alpha-olefin with amorphous and semi-crystalline blocks .
• All of these polymers or copolymers may further contain various agents, such as slip and antiblocking agents, antioxidants and stabilizers.
• the central layer “B” since the central layer “B" is the thickest, and is not in contact with the lips of the die, it can be used to recycle the waste of the multilayer materials recovered in the process, before drawing or after stretching, or potentially after the assembly steps.
• the amount of recycled multilayer materials in the central layer “B” may vary from 0 to 30% by weight, and is preferably between 0 and 15% by weight.
• the microporous skin layer "A" according to the invention is formed from at least one polyolefinic copolymer having a modulus E of less than 50 mPa (ASTM 882).
• This copolymer is chosen from the group formed by polar copolymers based on ethylene and / or grafted polyolefin polymers.
• Such polar copolymers and grafted polyolefin polymers show crystallinity levels that are different from those of the homopolymer versions: they exhibit greater water vapor transfer properties and improved softness properties for the layer under consideration. ".
• the permeability to gases and to water vapor of the layer "A" is measured by the rate of water vapor transmission (expressed in g / m 2/24 hours at a given temperature and a given relative humidity, example at 38 ° C and 90% for a given thickness).
• the properties of softness to the touch are measured (according to the ASTM D882 touch test) by a module E which must be less than 50 mPa.
• the polar ethylenic copolymer used in the production of the "A" layer is a copolymer composed of ethylene and at least one polar-type comonomer chosen from the group consisting of the family of vinyl esters and from the family of the acids. and acrylic and methacrylic esters.
• the polar comonomer may be selected from the group consisting of vinyl acetate, vinyl propionate, acrylic acid, methacrylic acid and their esters such as acrylates having 4 to 8 carbon atoms.
• One or more of these comonomers can be used simultaneously.
• copolymers of ethylene and at least one polar comonomer are formed by at most 30% by weight of comonomer.
• the copolymers of ethylene and at least one polar comonomer must have a melt index in the range of 1 to 10 g / 10 min under standard conditions (MFI ASTM standard D 1238 - 2.16 kg - 190 ° C). VS).
• the grafted polyolefin polymers used in the production of the "A" layer can be manufactured by chemical grafting using acrylic acid, methacrylic acid, maleic anhydride and alkyl acrylates and methacrylates in which the Alkyl is a C1 to C8 hydrocarbon chain.
• melt index of such graft polymers is in the same range as the previously mentioned polar copolymers.
• All of these polymers or copolymers may contain slip and antiblocking agents as well as antioxidants and stabilizers.
• the skin / adhesion layer "C" which will become microporous during drawing, comprises at least one adhesion binder and / or a thermoplastic polyolefin homopolymer and / or copolymer and at least one less a particulate charge.
• polystyrene resins are selected from the group consisting of polyethylenes, and preferably low density linear polyethylenes and / or polypropylenes and / or copolymers of ethylene-propylene and ethylene and alpha-olefin.
• the homopolymeric and / or copolymeric polyolefinic components of the microporous "C" skin layer are linear low density polyethylenes of between 0.880 and 0.940, copolymers of ethylene and of alpha-olefinic comonomers, such as those of C4 to C4.
• microporous films have a modest expandable capacity and a low tear resistance, they are often combined with a substrate which may for example be a nonwoven fabric, to improve their mechanical strength.
• the adhesive agent / binder present in the skin / adhesion layer "C" is chosen from the group of copolymers of ethylene and of polar or non-polar comonomers, copolymers of propylene and polar comonomers. or non-polar and / or homopolymers or copolymers (based on ethylene or propylene) grafted.
• the nonpolar copolymers may be chosen from the group of elastomers, previously described for the central layer "B".
• the adhesive / binder agent is introduced into the composition of said layer in a proportion of 2 to 20% and preferably 5 to 15% by weight.
• the polar copolymers they can be chosen from the group previously described for the skin layer "A".
• the skin / adhesion layer "C" according to the invention comprises from 30 to 80% by weight and preferably from 45 to 55% by weight of particulate fillers.
• These various fillers mentioned previously for layer “B” comprise organic or inorganic fillers but are preferably chosen from the group of mineral fillers comprising calcium carbonate, barium sulfate, silica, alumina, kaolin, talc and very preferably calcium carbonate.
• the average diameters of the particulate fillers are chosen between 0.2 and 3 ⁇ m, and preferably between 0.8 and 1.5 ⁇ m for the skin / adhesion layer "C", in order to return the thin gauge to the end of said layer "C".
• the multilayer precursor film is extruded into a die and is attached to the cooling roll by means of a vacuum box and / or an air knife.
• the multilayer precursor film is subsequently reheated and stretched between at least two (primary and secondary) draw roll systems.
• a thermal stabilization step is integrated in the production line, in order to release the tensions created in the film during the drawing step.
• a subsequent printing step and a film embossing step may also exist within the scope of the invention.
• the multilayer film can be made using a coextrusion chain for a cast film, or a coextrusion line for a blown cast.
• the melting temperature of the polymer material can be set between about 200 ° C and 250 ° C, depending on the setting of the extruder and the temperature setting of the Faculty.
• the precursor multilayer film can be coextruded and fixed as previously evoked to the cooling roll by means of an air knife and / or a vacuum box.
• the precursor multilayer film is rapidly cooled.
• the temperature of the multilayer precursor film, when leaving the cooling roll, is set between 15 ° C and 60 ° C.
• the breathable multilayer film can also be manufactured on a blown film coextrusion line.
• the molten polymer is extruded through an annular multilayer die and then blown into a bubble which is cooled by air directed through an air ring.
• the melting temperature of the polymeric material can be set between 150 ° C and 240 ° C.
• the height of the cooling chain (the cooling chain corresponds to the change in haze resulting from the solidification of the molten polymer) is an important parameter to control. This height of the cooling chain is normally set between 10 and 80 cm from the surface of the die.
• the blowing ratio corresponding to the ratio between the diameter of the bubbles and the diameter of the die is another parameter of the process to be controlled: this blowing ratio controls the orientation of the cross direction. This blowing ratio normally varies from about 1.5 to 4.0.
• the bubble is then folded to form a flat film coated and wound on a roll or split and wound into two separate rolls.
• the speed of the chain is between 20 and 150 m / min for a precursor film of 100 to 20 microns.
• the precursor film is stretched, similar to the step described in the extrusion technology of a multilayer film by casting.
• the filler material When a monolayer film comprising particulate fillers is extruded, the filler material accumulates on the extruder die lips, and blocks the extrusion process.
• the pile at the die level affects aspects of the film and creates furrow lines that reduce the strength of the film.
• the pile on the extruder die after a few hours of use is such that the extruder must be stopped and the heaped residues must be removed mechanically from the lips of the extruder. extruder.
• Such a stop for this type of process is very expensive and time consuming. This is why multilayer films which, when extruded, cause less pile on the lips of the die, are particularly sought after.
• the skin layer has no particulate filler and that the levels of moisture and volatile matter in the materials used are well controlled: because when a high content of Moisture and volatile matter in the molten polymer, the phenomenon of accumulation on the die accelerates and becomes very disturbing.
• one of the objects of the invention is to control the level of material accumulation on the die by degassing the molten polymer entering the formation of each layer to remove moisture and volatile materials during extrusion.
• Another object of the invention is to remove by degassing during extrusion the volatiles and moisture present which, under the effect of heat can be released and prevent the ability to control the formation of holes giving to the film its microporosity.
• the degassing step must be performed under vacuum conditions of less than 200 hPa in each of the extruders.
• the edge cut-outs resulting from the production of the breathable film can be recycled to the core layer. This is why it is desirable to degas the recycled material which may contain air included.
• This degassing operation is performed in an extruder dedicated to recycling and provided with a degassing means.
• Polymeric raw materials and particulate fillers may be desirably dried prior to extrusion as well as polymeric raw materials containing hygroscopic fillers.
• the highly charged precursor film when stretched in a controlled manner, produces a much thinner microporous film with a much thinner gauge, which has the desired properties of breathability and liquid impermeability.
• the extrusion and said drawing steps are carried out in such a way that the multilayer microporous film obtained has a thickness of at most 40 ⁇ m and preferably at most 25 ⁇ m.
• the multilayer precursor film exiting the cooling roll Prior to stretching, the multilayer precursor film exiting the cooling roll is warmed to the proper temperature for stretching and then stretched to form a breathable multilayer film.
• the coextruded precursor multilayer film can be stretched by any conventional method, for example by monoaxial or biaxial stretching.
• the precursor multilayer film is stretched in one direction, which is that of the machine (longitudinal direction).
• the drawing is carried out between at least two roller systems operating at different speeds of rotation in a standard drawing unit.
• the multilayer precursor film is drawn at a temperature of between 20 ° C and 95 ° C, and the draw ratio is between 1: 1.5 and 1: 6.
• the stretching of the multilayer precursor film can be carried out in one or more steps, followed by a possible thermal stabilization step.
• the drawing roll systems operate at different rotational speeds, in order to obtain, for example from a precursor film of 80 ⁇ m, a thinner film of for example 20 ⁇ m, corresponding to a monoaxial stretch ratio of 4: 1, dependent on relaxation; the speed ratio between the roll systems is known as the draw ratio: this ratio of speed is measured between the input and output roller systems of the draw zone.
• draw ratio this ratio of speed is measured between the input and output roller systems of the draw zone.
• the greater the distance between the two roll systems the greater the reduction in the width of the stretched film.
• the breathable film is thermally stabilized by releasing tensions by passing over heated roller systems.
• the temperature stabilization temperatures are between 30 ° C and 90 ° C for polyethylene and 30 ° C and 120 ° C for polypropylene.
• the multilayer breathable film according to the invention can also undergo an embossing step after stretching: this embossing gives a softer feel and reduces the gloss of the film. This embossing takes place between two rollers set at a temperature of 35 ° C to 100 ° C.
• the multilayer breathable film according to the invention has a moisture vapor transmission rate of water of at least 500 g / m 2/24 hours (at 38 ° C, 90% relative humidity) and preferably between 2000 and 5000 g / m 2/24 hours (at 38 ° C, 90% relative humidity) without losing its impermeability to liquids.
• the multilayer breathable film according to the invention can be used in the production of the rear film (backsheet) of a diaper for children, incontinent adults and disposable hygiene articles or assembled with a rolled nonwoven and used as a backsheet. that laminated product for the back film of a diaper for children, incontinent adults and disposable hygiene items.
• backsheet rear film
• the breathable multilayer film has a thickness of less than 40 ⁇ m and preferably less than 25 ⁇ m.
• this example relates to the production of a microporous multilayer film with asymmetric structure, ABC.
• the film is likely to be used as a backsheet in disposable hygienic products.
• the layer “A” which consists of a copolymer of ethylene and methyl methacrylate, offers a soft touch, while the layer “C” polypropylene allows welding / thermal lamination.
• the central layer "B" (intermediate) contributes to the transmission of water vapor.
• each layer was adjusted by means of a microscope. To do this, each layer was colored slightly, and the resulting film was cut after extrusion stretching: the thickness of each layer was controlled and adjusted by means of microscopic measurements.
• the raw materials have been formulated to be heat stable according to the formulations of the state of the art.
• CaCO 3 was premixed in the LLDPE "Dowlex 2035" formulation and in the PP blend of "Daplen K20333" and “Daploy HM 110F” on a twin-screw extruder with orifices. The compound was dried at 80 ° C for about 4 hours prior to film production.
• the three-layer precursor film was cast by coextrusion on a cooling roll and fixed by an air knife and a vacuum box. The latter was also used to evacuate the smoke from the die lips by means of a suction device.
• Extruder temperatures were set between 180 ° C and 230 ° C, with the temperature of the adapter and die slightly above 235 ° C. An automatic die was used for precise control of the gauge. A thickness tolerance of less than ⁇ 4% is achieved. The melting temperature was measured at about 230 ° C.
• the multilayer precursor film with a thickness of 80 ⁇ m was produced at a chain speed of about 25 m / min.
• the film After being stretched in a ratio of 4: 1, the film reached a thickness of 20 .mu.m and a breathability of approximately 2500 g / m 2/24 hours (at 38 ° C with a relative humidity of 90%).
• the skin layer containing the "Lotryl" raw material has been placed in such a way that it is in contact with the cooling roll, thus preventing the deposit of CaCO 3 on the roll.
• edge cutouts were removed from the process and regranulated in a degassing extruder operating at a vacuum level of less than 200 hPa.
• the recycled granules were incorporated into the core layer "B" in a weight ratio of 10%.
• embossing was applied to the film by heating and compressing the film under high pressure in a suitable embossing means.
• the embossing rolls had been engraved according to the desired pattern.
• the film was cooled in line and stored as a finished product in the form of a roll.
• This example relates to the production of a microporous multilayer film with symmetrical structure CBC according to the state of the art.
• the extruder flow conditions representing the distribution of the layer thickness in%, were set at 15:70:15.
• the materials were introduced as ready-to-use compounds that were made in a degassing twin-screw extruder, in order to reduce the moisture content.
• the compounds were produced under the same conditions as for Example I.
• the polymeric material used consisted of a dry blend comprising 52% CaCO 3 , 38% “Dow Elite 5200” and 10% “Dow SC 7641".
• the precursor film was cast on a cooling roll, as in Example I.
• the melting temperature was about 235 ° C
• the temperature of the die was set at 230 ° C.
• the chain speed was about 30 m / min for the production of the 60 ⁇ m thick multilayer precursor film.
• the 3-layer 60 ⁇ m precursor film After stretching in a ratio of about 3: 1, the 3-layer 60 ⁇ m precursor film had a thickness of 20 ⁇ m at a winding speed of 90 m / min.
• the transmission rate of the water vapor was 3000 g / m 2/24 hours (at 38 ° C with a relative humidity of 90%).
• the microporous film was cut along the chain before winding, then it was hot rolled on one of its faces on a nonwoven polypropylene. The other side of the film was glued on a disposable item.
• the hot bonding force between the two components, the multilayer breathable film and the nonwoven fabric was excellent, as shown by tearing of the threads during peeling.
• This example relates to the production of a multilayer microporous film symmetric structure ABA according to the invention.
• Table III Thickness distribution 10% 80% 10% Polymer formulation in each layer "A” layer “B” layer “A” layer Polymer 1 100% EMA “Lotryl 20 MB08” 50% LLDPE “Dowlex 2035” 100% EMA “Lotryl 20 MB08” Polymer 2 Charge 48% CaCO 3 "Filmlink 520" Additive 2% TiO 2
• the extruder flow conditions representing the distribution of the layer thickness in% were set at 10:80:10.
• the chain speed was about 20 m / min to produce a 100 ⁇ m precursor film.
• the draw ratio was about 4: 1, resulting in a 25 ⁇ m film at a winding speed of 80 m / min.
• the extruder temperatures feeding the "A" layer were set at approximately 220 ° C in the final zone while the temperature in the last extruder zone feeding the "B” layer was set at 240 ° C.
• the temperature of the die was below 230 ° C.
• the film produced had a very soft touch surface and a moisture vapor transmission rate of water of about 1500 g / m 2/24 hours (at 38 ° C with a relative humidity of 90%).
• TiO 2 in the core layer improved the opacity of the film.
• the Montell "Adflex X102S” is a polypropylene elastomeric copolymer with a melt index of 8.0 g / 10 min (MFI ASTM D 1238 standard - 2.16 kg - 230 ° C) and a density of 0.890. It allows compatibility between polymeric materials, thus improving the adhesion between the "A” layer and the "B” layer and also offers a softer feel.
• the extruder feeding layer "A” was set at a temperature of 220 ° C.
• the melting temperature was set at 240 ° C.
• a precursor film of 80 ⁇ m was produced at a speed of 25 m / min.
• the film was stretched approximately in a ratio of 4: 1 in order to obtain a breathable film of approximately 20 ⁇ m in thickness.
• the film had a moisture vapor transmission rate of water of 3200 g / m 2/24 hours (at 38 ° C with a relative humidity of 90%).

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• Laminated Bodies (AREA)
• Extrusion Moulding Of Plastics Or The Like (AREA)
• Separation Using Semi-Permeable Membranes (AREA)
• Manufacture Of Porous Articles, And Recovery And Treatment Of Waste Products (AREA)

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• 1999
  • 1999-12-28 FR FR9916598A patent/FR2802849B1/fr not_active Expired - Lifetime
• 2000
  • 2000-12-28 AU AU31815/01A patent/AU3181501A/en not_active Abandoned
  • 2000-12-28 WO PCT/FR2000/003729 patent/WO2001047710A1/fr active IP Right Grant
  • 2000-12-28 ES ES00991293T patent/ES2248166T5/es not_active Expired - Lifetime
  • 2000-12-28 AT AT00991293T patent/ATE301543T1/de not_active IP Right Cessation
  • 2000-12-28 EP EP00991293A patent/EP1250225B2/fr not_active Expired - Lifetime
  • 2000-12-28 DE DE60021918T patent/DE60021918T3/de not_active Expired - Lifetime

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